Electric cable and method of manufacturing same



Feb. 19, 1929. 1,702,332

R. APT

ELECTRIC CABLE AND METHOD OF MANUFACTURING SAME Filed Jan. 1926 ample,

Patented. Feb. 19, 1929.

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nnncrmc CABLE AND nnrnonor umurecroame sin Application med January 9,1926, Serial No. 80,376, and in Germany January 27, 1985.

Lead-covered electric cables air power transmission and telephonicpurposes have for a long time been produced by enclosing the ing to theexternal diameter of the cable. The above described mode of manufacturenecessitates the cables being of rather great weight which increases thecost of transport and laying. The thick lead covering however in certaincases introduces disadvantages of another kind. In polyphase currentcables it is true, that owing to the twisting or stranding, the severalcable elements of the core are symmetrically arranged, but nevel thelessinductive action on the lead covering is not wholly eliminated, so thateddy currents are formed therein which occasion losses. Such efiects inthe lead covering become manifest to a specially great extent in thosesingle cables for alternating or polyphase current power transmissionwhich are preferably emplo ed for yery high voltage instead of the cabes with a core of three elements. In the transmission of alternatingcurrents through single cables, very considerable voltages are inducedin the lead covering'an'd these give rise to eddy-currents. 1

The leadcovering of these cables, however, must for mechanical reasons,be chosen specially thick, be provided at all for such single cables inconsequence of the magnetic action. Heavy losses accordingly arise inthe thick lead covering of cables so conditioned with respect to theirconstruction, which losses militate against the utility of a singlecable (which per se is highly preferable) wh'en transmitting hightension alternatin currents. The lead covered cables manu acturedheretofore have the further drawback-;--that in consequence of the factthat armours made as above described constitute only inefiectiveelectric insulation, stray currents penetrate I the lead covering fromdistant circuits, for exfrom street railways, and in certaincircumstances these cause extensive damage. Moreover, the lead coveringsare readily attacked by chemical action, for example, in

since armours of iron cannot chemical works and lime-pit plants and thetween adjacent cables, which arcs may likewise cut away the-lead coverinx Lead covered telephone ca les are either drawn as cables into cementconduits, or, being rov'ided with the usual iron armour, are em dded inthe ground. In these cables also the lack ofa suitable protective jackethas been found to lead to trouble. Lead is attacked chemically b cementand when the cable is laid directly inthe ground, stray currents andchemical action may come intogplay, as in the case of ld'rge currentcables.

, The fjsubjectm'atter ofthe present invention is a lead covered cablewherein the above described disadvantages are avoided, in that the leadcoveringis in; part replaced ENT OFFICE. v

by a covering of rubber. The] lead covering.

can thus be of a very-small thicknes's'so die mensioned'that it is justwithin the possibil ity of applying a seamless covering. En-

.thickness which is caused to unite with or tightly enclose and protectthe lead covering from mechanical, chemical andelectrical ac.-

tion and the duty of which, at the same time, is to replace thestrip-iron armour. -Where the danger of pronounced mechanical actionappears to require it, there'may' of course be arranged over the rubberjacketan armour of iron. In order to secure as tight an enclosure aspossible itis preferred .to so compose .therubber mixture that atvulcanization an intimate connection between lead covering and rubbercoatingis produced. This may be effected, for example, by mixing withthe rubber mixture an excess of sulphur so that when there is contactwith the lead of the lead covering, sulphide of lead is formed,

material of the cable core

